JP2019178383A - Method for producing metal particle dispersion liquid - Google Patents

Abstract

To provide a metal particle dispersion liquid with high storage stability.SOLUTION: A method for producing a metal particle dispersion liquid has a particle preparation step of reducing a metal salt in liquid containing fine foam to prepare metal particles, and a cleaning step of cleaning the metal particles prepared in the particle preparation step with cleaning liquid.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a metal particle dispersion.

  Metal particles are used in various applications as catalyst materials, semiconductor materials, conductive materials, and the like. For example, conductive materials are used for electrodes, circuits, antistatic transparent coatings, electromagnetic shielding transparent coatings, capacitor electrodes, and the like of various electronic devices (see Non-Patent Document 1).

  As a method for producing such metal particles, a method for producing metal particles by reducing a metal salt in an organic solvent has been proposed (see, for example, Patent Documents 1 and 2). However, the metal particles obtained by the method using the organic solvent have a problem of low conductivity.

  Thus, in order to obtain metal particles having higher conductivity, attempts have been made to produce metal particle dispersions in water. However, metal particles are easily oxidized and ionized, and stable metal particle dispersions can be obtained. difficult.

JP 2005-281781 A JP 2008-75181 A

Author of Metal and Semiconductor Nanoparticles, Author, The Chemical Society of Japan, Publisher, Ryosuke Sone, Publisher, Kagaku Dojin (2012)

  An object of the present invention is to provide a metal particle dispersion having high storage stability.

It has been found that by reducing the metal salt in a liquid containing microbubbles, the oxidation and ionization of the metal particles are suppressed, and the storage stability of the metal particle dispersion is dramatically improved (lengthened).
The liquid containing microbubbles has a higher dissolved oxygen concentration and a higher oxidation-reduction potential than conventionally used degassed (deoxygenated) treated water with an inert gas such as N ₂ bubbling water, and is therefore used in a reduction reaction system. This is generally considered undesirable. However, surprisingly, by reducing the metal salt using the liquid containing the microbubbles, the storage stability of the produced metal particle dispersion is improved, and a coating liquid pot using the metal particle dispersion is used. I found that my life improved.

  That is, the present invention includes a particle preparation step of preparing metal particles by reducing a metal salt in a liquid containing microbubbles, and a cleaning step of cleaning the metal particles prepared in this particle preparation step with a cleaning liquid. The present invention relates to a method for producing a featured metal particle dispersion. The present invention also relates to a method for producing a coated substrate, wherein a coating liquid for forming a coating containing metal particles prepared by this production method is applied onto the substrate.

  A metal particle dispersion having high storage stability in which oxidation and ionization of metal particles are suppressed can be obtained.

  The method for producing a metal particle dispersion of the present invention comprises a particle preparation step of preparing metal particles by reducing metal salt in a liquid containing microbubbles (hereinafter sometimes referred to as a reaction solution), and a particle preparation step. And a cleaning step of cleaning the metal particles with a cleaning liquid. This manufacturing method may include other steps before and after the above steps. For example, a coarse particle removing step for removing coarse particles may be included after the cleaning step.

By using a liquid containing microbubbles in the particle preparation step, it is possible to suppress the oxidation and ionization of the metal particles contained in the dispersion and improve the storage stability of the metal particle dispersion. Moreover, the pot life of the coating liquid using this metal particle dispersion can be prolonged.
In this manufacturing method, alloy particles can be obtained with high yield. Furthermore, the film using the metal particles has high conductivity. Although these reasons are not well understood, the microbubbles contained in the reaction solution promote the reduction reaction from the metal salt to the metal, and the protection for the metal particles to exist as a metal without being oxidized. It is assumed that it is due to the action.

[Method for producing metal particle dispersion]
<Particle preparation process>
In the particle preparation step, metal particles are prepared by reducing a metal salt in a liquid containing microbubbles as described above. The liquid containing microbubbles may be an organic solvent or water. However, the effect is more exhibited in the case of water. If an oxidizing gas such as oxygen is present in the reaction solution, the metal may be oxidized. Therefore, it is desirable to reduce the oxidizing gas as much as possible in the space where the reaction solution and the reaction solution are in contact. This step is preferably performed in a state purged with an inert gas such as N ₂ gas or a rare gas in order to suppress the mixing of the oxidizing gas. However, in this production method, bubbling of the reaction solution with an inert gas is not necessarily performed.
Here, as the oxidizing gas, oxygen, ozone, carbon dioxide gas, nitrogen monoxide, dinitrogen monoxide, nitrogen dioxide, fluorine, chlorine, chlorine dioxide, nitrogen trifluoride, chlorine trifluoride, silicon tetrachloride, silicon tetrachloride, Examples thereof include oxygen fluoride and perchloryl fluoride.

  The reaction solution in this step has an oxidation-reduction potential of preferably −50 mV or less, and more preferably −100 mV or less. The pH is preferably 4.0 to 11.0, and more preferably 4.5 to 7.0. By reducing the metal salt within the range of the oxidation-reduction potential and pH, the metal particles are generated smoothly. Moreover, as reaction temperature, 10-80 degreeC is preferable.

<Microbubbles>
The microbubbles are preferably microbubbles (micronanobubbles) having an average bubble diameter of 40 nm to 10 μm. Such microbubbles include at least one of so-called nanobubbles having a bubble diameter of 40 to 100 nm (0.1 μm) and so-called microbubbles having a bubble diameter of 0.1 to 10 μm, and preferably include both. . The upper limit of the average bubble diameter of the microbubbles is preferably 500 nm, more preferably 350 nm, and even more preferably 200 nm. Further, the lower limit of the average bubble diameter of the microbubbles is preferably 50 nm, more preferably 60 nm, and even more preferably 65 nm.

The content of microbubbles is preferably 1.0 × 10 ³ pieces / mL or more, more preferably 1.0 × 10 ⁵ pieces / mL or more, and further preferably 1.0 × 10 ⁸ pieces / mL or more. The upper limit is not particularly limited, but is preferably 1.0 × 10 ¹¹ pieces / mL, more preferably 5.0 × 10 ¹⁰ pieces / mL, and further preferably 1.0 × 10 ¹⁰ pieces / mL.

  The average bubble diameter and the number of bubbles of the microbubbles are obtained by analyzing the Brownian movement speed of the bubbles in the liquid by the nanoparticle tracking analysis method (NTA). For example, it can be measured using “Nanosite NS300” manufactured by Malvern.

  The gas that forms the microbubbles is preferably a non-oxidizing gas. Specifically, at least one of nitrogen, hydrogen, and a rare gas is preferable.

《Metal salt》
The metal salt that is the raw material of the metal particles is a metal of one kind selected from the groups 4, 5, 6, 8, 9, 10, 11, 13, 13, and 15 of the periodic table. Salt is used. Examples of the salt include chloride salts, nitrates, sulfates, and organic acid salts.

  Preferred metal elements are Ti for Group 4, Ta for Group 5, W for Group 6, Ru for Group 8, Co, Rh for Group 9, Ni, Pd, Pt for Group 10, Cu, Ag, Au for Group 11, Group 13 is exemplified by Al, In, group 14 is Sn, and group 15 is exemplified by Sb. In particular, even a metal that is easily oxidized other than Au or Ag can suppress oxidation and obtain metal particles in a high yield.

<Reducing agent>
The reduction reaction in the particle preparation step is usually performed using a reducing agent.
Examples of the reducing agent include ferrous sulfate, NaBH ₄ , hydrazine, hydrogen, alcohol, trisodium citrate, tartaric acid, sodium hypophosphite, formic acid, LiBH ₄ , LiAlH ₄ , and diborane. Of these, trisodium citrate, tartaric acid, and formic acid are preferable. These have the functions of both a reducing agent and a stabilizer. For this reason, the process for removing impurities is reduced and the stability is improved.

  Although the usage-amount of a reducing agent changes also with the reducibility of a metal salt, 0.5-10 mol is preferable with respect to 1 mol of metal salts, and 1-5 mol is more preferable. Here, when the reducing agent is less than 0.5 mole relative to 1 mole of the metal salt, the reduction is insufficient and the desired metal particles may not be obtained. When the reducing agent exceeds 10 moles with respect to 1 mole of the metal salt, metal particles having a particle size larger than necessary may be generated.

<Organic stabilizer>
In the particle preparation step, an organic stabilizer is preferably used. By adding the organic stabilizer, the organic stabilizer is adsorbed to the metal salt, the dispersibility of the metal salt is improved, and the metal salt can be reduced more smoothly. Further, the generated metal particles are stably dispersed in the dispersion medium.

  Any organic stabilizer may be used as long as it can be adsorbed on a metal salt or metal particles to enhance dispersion stability. For example, gelatin, polyvinyl alcohol, polyvinyl pyrrolidone, vinyl acetate, polyacrylic acid, carboxylic acid compounds and the like are suitable. Among these, a carboxylic acid compound having a carboxyl group having a large interaction with the surface of a metal salt or metal particles is preferable, and a polyvalent carboxylic acid compound is particularly preferable.

  Carboxylic acid compounds include, for example, anthonic acid, hydroxyanthracenecarboxylic acid, hydroxynaphthoic acid, gallic acid, crestic acid, parahydroxybenzoic acid, ortho-acetylsalicylic acid, malic acid, mandelic acid, gluconic acid, citric acid, tartaric acid, lactic acid Benzenecarboxylic acid, formic acid, acetic acid, butanoic acid, propionic acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, 9-hexadecenoic acid, Examples include heptadecanoic acid, octadecanoic acid, glycolic acid, L-ascorbic acid, fumaric acid, maleic acid, adipic acid, and salts thereof. These may be used alone or in combination of two or more. Among these, citric acid or a salt thereof is preferable, and trisodium citrate is particularly preferable because of its large interaction with the metal salt or the surface of the metal particles.

  0.5-10 mol is preferable with respect to 1 mol of metal salts, and, as for the usage-amount of an organic stabilizer, 1-5 mol is more preferable. Here, when the organic stabilizer is less than 0.5 mole relative to 1 mole of the metal salt, the amount of the organic stabilizer adsorbed on the metal salt is too small, and the dispersibility of the metal salt becomes insufficient. There is a possibility that salt reduction and metal particle dispersibility may be insufficient. Conversely, when the organic stabilizer exceeds 10 moles per mole of the metal salt, the dispersibility and reducibility of the metal salt and the dispersibility of the metal particles are not particularly improved, and the organic stability in the subsequent washing step is not improved. Extra work may be required for the removal of the chemical agent and the wastewater treatment.

<< pH adjuster >>
A pH adjuster can be used so that the pH of the reaction solution in the particle preparation step is 4.0 to 11.0. As the pH adjusting agent, a mineral acid or an organic acid is suitable. Of these, organic acids having C _{1 to} C ₃ carbon atoms are preferred. In addition, the said organic stabilizer may serve as the function of a pH adjuster.

<Washing process>
In the washing step, the metal particles prepared in the particle preparation step are washed with a washing liquid. In this step, desalting is performed and the organic stabilizer is removed. Here, the salt is a substance other than the metal particles generated by the reduction treatment of the metal salt, and exists as ions in the reaction solution. Specific examples include metal ions such as sodium and iron, boron ions, chloride ions, nitrate ions, sulfate ions, and organic acid ions.

  The cleaning liquid is suitably water or alcohol, and may contain other components. In addition, it is preferable to use at least one of a bubbling liquid obtained by previously bubbling an inert gas to remove oxygen and a liquid containing microbubbles as the cleaning liquid. ) Is particularly preferred. The details of the liquid containing microbubbles are the same as the liquid (reaction liquid) containing microbubbles used in the particle preparation step. Moreover, it is preferable that the metal particle dispersion manufactured after washing | cleaning also contains a microbubble.

  By washing metal particles with a cleaning solution containing microbubbles, the metal particles are prevented from ionization and oxidation, and the storage stability of the metal particle dispersion and the pot life of the coating solution using this metal particle dispersion are dramatically improved. Can be improved. Further, the dispersibility of the produced metal particles is improved, and the amount of the organic stabilizer in the final dispersion can be reduced. Therefore, when the coating film is formed, the metal particles come into direct contact with each other, the resistance at the particle boundary is reduced, and as a result, a coating film having high conductivity can be formed.

  Examples of the cleaning method include a decantation method and a cleaning method using an ultra-thin film or a ceramic film. In the method by decantation, for example, metal particles are recovered from the metal particle dispersion prepared in the particle preparation step, and the recovered metal particles are immersed in a cleaning solution for cleaning (desalting). The cleaning liquid preferably contains a high concentration organic stabilizer. As a result, the metal particles are appropriately aggregated, and impurities such as nitrate ions and sulfate ions are eluted in the supernatant to remove the impurities. Furthermore, it is preferable to refine | purify using an ion exchange resin. Note that the organic stabilizer used in the washing step may be the same as or different from that used in the particle preparation step.

  In the present invention, even when a cleaning solution having a relatively low concentration of the organic stabilizer is used, impurities can be sufficiently removed, and the subsequent treatment with an ion exchange resin can be simplified (reduction in the amount of resin). Metal particles can be produced. In addition, it is possible to reduce the number of times of washing, and this can also efficiently produce metal particles. By simplifying the cleaning process, loss of metal particles is reduced and the yield can be improved. Furthermore, since the induction of oxidation of the metal particles is suppressed by simplifying the cleaning process, the film formed using the metal particles has high conductivity.

<Coarse particle removal process>
After the washing step, it is preferable to remove coarse particles by centrifugation or the like.

[Metal particle dispersion]
The metal particle dispersion liquid of the present invention is characterized in that metal particles are dispersed in a liquid containing microbubbles. The details of the liquid containing microbubbles are the same as the liquid (reaction liquid) containing microbubbles used in the particle preparation step. Further, examples of the metal particles include metal particles of Group 4, Group 5, Group 6, Group 8, Group 9, Group 10, Group 11, Group 13, Group 14 and Group 15 of the Periodic Table. A plurality of kinds of metal particles may be mixed and used. This metal particle dispersion can be produced by the production method described above.
As the dispersion medium, water or an organic solvent is suitable. Here, the organic solvent is not particularly limited, but alcohols are preferable from the viewpoint of ease of processing as a coating solution and ease of production of a coated substrate. Of these, methanol and ethanol are preferable.

  The storage stability of the metal particle dispersion is usually from several hours to one month, although it depends on the metal species when produced using only a solvent bubbled with an inert gas. In contrast, the storage stability of the metal particle dispersion of the present invention exceeds 3 months. This is considered to be due to some action acting between the microbubbles and the metal particles, unlike the action when the bubbles simply exist.

  In the current technology, it is difficult to measure the average bubble diameter and the number of bubbles in a dispersion in which metal particles and microbubbles coexist. Therefore, the average bubble diameter and the number of bubbles are determined by removing metal particles with an ultrafiltration membrane and measuring the minute bubbles contained in the filtrate. That is, the average bubble diameter and the number of bubbles in the present invention are those obtained by measuring a filtrate that has passed through an ultrafiltration membrane having a molecular weight cut-off of 4000.

The redox potential (ORP) of the metal particle dispersion is preferably 0 to 300 mV, more preferably 100 to 250 mV. Here, when the ORP is less than 0 mV, the dispersibility of the metal particles may become unstable due to the reduction field. Conversely, when the ORP exceeds 300 mV, the metal particles may be oxidized.
Moreover, pH is 4.0-7.0 normally, and 4.5-6.5 are preferable. Here, when pH is less than 4.0, it exists in the state of an ion and a metal particle may not be obtained. Conversely, when the pH exceeds 7.0, the metal particles may aggregate due to the high salt concentration.

  The electric conductivity of the metal particle dispersion is preferably 10 to 500 μS / cm, more preferably 50 to 300 μS / cm. Here, when the electrical conductivity is less than 10 μS / cm, there are cases where the amount of the dispersant is small and the storage stability is lowered (life is short). On the other hand, when the electrical conductivity exceeds 500 μS / cm, the salt concentration increases, so that the storage stability may be lowered. Moreover, even if a conductive film is formed, the conductivity may deteriorate.

  The content of each impurity in the metal particle dispersion is preferably 100 ppm or less, more preferably 80 ppm or less, and even more preferably 50 ppm or less with respect to the metal particles. Here, if it exceeds 100 ppm, the salt concentration increases, so that the storage stability may decrease. Moreover, even if a conductive film is formed, the conductivity may deteriorate. The impurities in the metal particle dispersion are substances other than metal particles, a dispersion medium, an organic stabilizer, and various additives. This is a substance other than the metal particles generated by the reduction treatment of the metal salt and exists as ions in the reaction solution. Specific examples include metal ions such as sodium and iron, boron ions, chloride ions, nitrate ions, sulfate ions, and the like.

  Moreover, 0.1-5 mass% is preferable with respect to a metal particle, and, as for the amount of organic stabilizers in a metal particle dispersion liquid, 0.2-3 mass% is more preferable. Here, when the organic stabilizer is less than 0.1% by mass with respect to the metal particles, the amount of adsorption of the organic stabilizer to the metal particles is too small, and the dispersibility of the metal particles may be insufficient. There is. On the other hand, when the organic stabilizer exceeds 5% by mass with respect to the metal particles, the cleaning is insufficient, the dispersibility of the metal particles is not improved, and the particles may rather aggregate. The content of the organic stabilizer contained in the metal particle dispersion can be determined by analyzing the amount of C (carbon) derived from the organic stabilizer.

The average particle diameter of the metal particles contained in this metal particle dispersion is preferably 3 to 200 nm, more preferably 5 to 70 nm. When the average particle diameter is 3 to 200 nm, a highly transparent conductive film can be obtained.
The average particle diameter of the metal particles is obtained as an average value obtained by taking an electron micrograph and measuring the particle diameter of any 500 particles.

  The metal particle dispersion of the present invention can suppress oxidation and ionization of metal particles. Therefore, even in an aqueous system, long-term storage stability that could not be realized conventionally can be realized. In addition, a long pot life that could not be realized with a coating solution using this metal particle dispersion can be realized. Furthermore, the metal particle dispersion of the present invention has a very low content of oxide particles and can produce a highly conductive coating. Here, the metal oxide is preferably not detected by X-ray diffraction. The content thereof is preferably 500 ppm or less, more preferably 200 ppm or less, and still more preferably 100 ppm or less with respect to the particles. If the content of the metal oxide exceeds 500 ppm, the storage stability of the dispersion is lowered, and the particles may aggregate and precipitate. Further, when the metal particles are ionized, they do not exist as particles in the liquid, and a desired film cannot be obtained even if this is used as a coating liquid.

[Coating liquid for film formation]
A coating liquid for forming a film can be produced using the metal particles contained in the metal particle dispersion of the present invention. Various conventionally known additives can be added to the coating liquid for forming a film.

  In the production of a substrate with a film, the coating liquid for forming a film is coated on the substrate, dried, and fired as necessary.

  Examples of the base material include base materials such as films and sheets made of glass, plastic, ceramic, metal and the like. Examples of the application method of the coating liquid include a dipping method, a spinner method, a spray method, a roll coater method, and a flexographic printing method. The film thickness is preferably about 30 to 300 nm, more preferably about 50 to 200 nm.

  The drying temperature is, for example, room temperature to about 90 ° C. The firing temperature is, for example, about 120 to 900 ° C, and may be about 150 to 350 ° C. Since the metal particles contained in the dispersion of the present invention have little adhesion of organic substances such as organic stabilizers, it is not necessary to remove the organic substances by baking at a high temperature such as 400 ° C. or higher. Thereby, aggregation and fusion of metal particles due to high-temperature firing can be prevented, and deterioration of haze of the resulting coating can be suppressed.

[Example 1]
<Particle preparation process>
Ultra pure water and N ₂ are brought into contact with a swirling flow type bubble generator (HYK-20-SD manufactured by Ligalic Co., Ltd.), and N ₂ micro-nano bubble water (average bubble diameter 70 nm, number of bubbles 240 million / mL). , PH 5.79 (25 ° C., the same applies hereinafter), electric conductivity 1.17 μS / cm, dissolved oxygen concentration (DO) 1.70 ppm, redox potential (ORP) 330 mV).
400 g of trisodium citrate dihydrate (organic stabilizer) was dissolved in 930 g of N ₂ micro / nano bubble water to prepare a solution (S1-1).
180 g of ferrous sulfate heptahydrate (reducing agent) was dissolved in 600 g of N ₂ micro / nano bubble water to prepare a solution (S1-2).
The solution (S1-1) and the solution (S1-2) were mixed and stirred for 30 minutes to prepare a solution A1.

A solution B1 was prepared by dissolving 76 g of copper (II) nitrate trihydrate in 600 g of N ₂ micro / nano bubble water. Thereafter, metal particles were separated and collected by a centrifuge from the dispersion obtained by adding the solution A1 to the solution B1 and stirring for 10 hours.

<Washing process>
Ultra pure water (pH 6.32, electric conductivity 0.05 μS / cm, DO 6.17 ppm, ORP 350 mV) was bubbled with N ₂ for 1 hour, and dissolved oxygen was removed from N ₂ bubbling water (pH 6.6, electric conductivity). Degree 0.6 μS / cm, DO 0.6 ppm, ORP 260 mV). The separated and recovered metal particles were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using N ₂ bubbling water and washed (desalted), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a concentration of 2.5% by mass in terms of metal was prepared using N ₂ bubbling water. Thereafter, deionization was performed using 10 g of the amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-1) having a concentration of 2.5% by mass in terms of metal.

[Average bubble diameter and number of bubbles]
For the fine bubbles in the metal particle dispersion (P-1), the metal particle dispersion is filtered through an ultrafiltration membrane (SEP-1013 molecular weight 4000, manufactured by Asahi Kasei) to remove the metal particles, and the microbubbles in the filtrate are removed. The average bubble diameter and the number of bubbles were measured. The average bubble diameter and the number of bubbles in the microbubbles were measured using the nanoparticle tracking analysis method for the Brownian movement speed of the bubbles in the liquid. Specifically, about 20 mL of a measurement sample (solution A1, solution B1 or metal particle dispersion (P-1) filtrate) is sucked into a measurement device (“Nanosite NS300” manufactured by Malvern), and nanoparticle Measured by tracking analysis method. In addition, the micro nano bubble water was measured by the said method as it was, without carrying out the filtration process.

Physical properties of the solution after reduction in the particle preparation step (pH, ORP), physical properties of the finally obtained metal particle dispersion (average bubble diameter and number of bubbles, pH, ORP, metal particle content and yield) Ratio, average particle size of primary particles, average particle size of secondary particles, presence or absence of metal oxides, content of impurities (Fe, Na, B, SO ₄ , NO ₃ ), amount of C (carbon), storage stability ) Is shown in Table 1 (the same applies to the following examples and comparative examples).

[Electric conductivity]
The electrical conductivity was measured by the AC two-electrode method. Specifically, the pH meter (Horiba, Ltd. F-74, electrode model number 3551-10D) was obtained by immersing the electrode in the liquid to be measured in the conductivity measurement mode. In addition, each liquid temperature of bubbling water, micro nano bubble water, and a metal particle dispersion was adjusted to 25 degreeC.

[Redox potential (ORP)]
The oxidation reduction potential (Oxidation Reduction Potential) was determined by immersing the electrode in a solution for measuring the electrode in the ORP measurement mode in the pH meter (F-74, manufactured by Horiba, Ltd., electrode model number 9300-10D). In addition, each liquid temperature of bubbling water, micro nano bubble water, and a metal particle dispersion was adjusted to 25 degreeC.

[Dissolved oxygen concentration (DO)]
The dissolved oxygen concentration was measured by the diaphragm type galvanic cell method. Specifically, a pH meter (Horiba Seisakusho OM-51, electrode model number 9520-10D) was measured in the conductivity measurement mode, and the electrode was immersed in the liquid to be measured and obtained under atmospheric pressure. In addition, each liquid temperature of bubbling water, micro nano bubble water, and a metal particle dispersion was adjusted to 25 degreeC.
[Yield of particles]
The yield of metal particles is calculated from the metal concentration in the metal dispersion measured by ICP for the amount of metal in the metal particle dispersion, and divided by the theoretical amount of metal calculated from the charged metal salt. Multiplied by 100.

[Average particle size of primary particles]
The average particle diameter of the metal particles was measured by an image analysis method. Specifically, using a transmission electron microscope (H-800, manufactured by Hitachi, Ltd.), the metal particle dispersion was dried on a collodion film of a copper cell for an electron microscope and photographed at a magnification of 250,000 times. The particle diameter of any 500 particles in the resulting photographic projection was measured, and the average value was taken as the average particle diameter of the metal particles.

[Average particle size of secondary particles]
The metal particle dispersion was directly put into a cell and measured by the microtrack method, and the average value (D50) was taken as the average particle diameter of the metal particles.

[Confirmation of presence or absence of metal oxide by X-ray diffraction]
The metal particle dispersion was kept in solution and analyzed by X-ray diffraction to confirm the presence or absence of metal oxide. The qualitative analysis of the sample by X-ray diffraction was performed with X-RAY DIFFRACT METER (SmartLab) manufactured by RIGAKU Corporation. Specifically, the sample is put in a cell and set in an apparatus, and the tube voltage is 45.0 kV, the tube current is 200.0 mA, the counter cathode Cu, the measurement range: start angle to end angle (2θ) from 5.000 ° to 70.000. The measurement was performed at a scan speed of 5.000 ° / min.
When no metal oxide peak is observed:
When a metal oxide peak is observed: ×

[ICP analysis]
For mass analysis of each element, chemical analysis was performed with an inductively coupled plasma spectrometer. Specifically, a metal particle dispersion was dissolved in concentrated nitric acid, and a solution adjusted to a concentration of 10 to 100 mass ppm with water was analyzed with SEQUENTIAL PLASMA SPECTROMETER (ICPS-8100) manufactured by Shimadzu Corporation.

[Ion chromatographic analysis]
The metal particle dispersion using ion exchange chromatography were diluted 100-fold with ultrapure water (manufactured by Tosoh TSKgel _SuperQ-5PW), were measured SO 4, Cl, NO _3, the concentration of.

[C (carbon) content measurement]
The carbon content in the metal particles was measured by drying the metal particle dispersion at 100 ° C. and using a carbon sulfur analyzer (EMIA-320V manufactured by HORIBA).

[Storage stability]
The presence or absence of oxidation of the metal particles and the change in conductivity were confirmed by X-ray diffraction (XRD) of the metal particle dispersion stored at 25 ° C.

<Preparation of coating solution for coating formation and substrate with coating>
The obtained metal particle dispersion (P-1) was diluted to 0.5% by mass with ethanol to prepare a coating liquid for film formation. This was applied to glass by a spin coat method, and then baked at 200 ° C. for 30 minutes in a nitrogen atmosphere to prepare a coated substrate. The conductivity of this coated substrate was measured with a Loresta (NSCP probe manufactured by Mitsubishi Chemical Corporation). Moreover, a part of the coating was peeled off with a cutter knife to create a step, and this step was measured with a laser microscope to obtain a film thickness. These results are shown in Table 1 (the same applies to the following Examples and Comparative Examples).

[Example 2]
<Particle preparation process>
Ultra-pure water and Ar are brought into contact with a swirling flow type bubble generator (HYK-20-SD manufactured by Ligalic Co., Ltd.), and Ar micro-nano bubble water (average bubble diameter: 70 nm, number of bubbles: 240 million / mL, pH 6) .25, electric conductivity 0.95 μS / cm, redox potential 300 mV, dissolved oxygen concentration (DO) 1.52 ppm, ORP 300 mV). 400 g of trisodium citrate dihydrate was dissolved in 930 g of this Ar micro / nano bubble water to prepare a solution (S2-1).
180 g of ferrous sulfate heptahydrate was dissolved in 600 g of Ar micro / nano bubble water to prepare a solution (S2-2).
The solution (S2-1) and the solution (S2-2) were mixed and stirred for 30 minutes to prepare a solution A2.

  A solution B2 was prepared by dissolving 76 g of copper (II) nitrate trihydrate in 600 g of Ar micro / nano bubble water. Thereafter, the solution A2 was added to the solution B2, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours using a centrifuge.

<Washing process>
Ultra-pure water (pH 6.32, electric conductivity 0.05 μS / cm, DO 6.17 ppm, ORP 350 mV) was bubbled with Ar for 1 hour to remove dissolved oxygen, and Ar bubbling water (pH 6.64, electric conductivity 0). 0.8 μS / cm, DO 0.51 ppm, ORP 260 mV).
The separated and recovered metal particles are immersed in 200 g of an aqueous solution of trisodium citrate having a concentration of 20% by mass prepared using Ar bubbling water and washed (desalted) by immersing the separated and recovered metal particles, and then separated by centrifugation again. It was collected.

  The metal concentration was quantified by ICP analysis, and an aqueous metal particle dispersion having a concentration of 2.5 mass% in terms of metal was prepared using Ar bubbling water. Thereafter, deionization was performed using 10 g of the amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-2) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (P-2) was used.

[Example 3]
<Particle preparation process>
In the same manner as in Example 1, N ₂ micro-nano bubble water was prepared.
400 g of trisodium citrate dihydrate was dissolved in 930 g of N ₂ micro / nano bubble water to prepare a solution (S3-1).
100 g of ferrous sulfate heptahydrate was dissolved in 500 g of N ₂ micro / nano bubble water to prepare a solution (S3-2).
The solution (S3-1) and the solution (S3-2) were mixed and stirred for 30 minutes to prepare a solution A3.

A solution B3 was prepared by dissolving 57 g of silver nitrate (I) in 300 g of N ₂ micro / nano bubble water. Thereafter, metal particles were separated and collected by a centrifuge from the dispersion obtained by adding the solution A3 to the solution B3 and stirring for 10 hours.

<Washing process>
N ₂ bubbling water was prepared in the same manner as in Example 1.
The separated and recovered metal particles were immersed in 200 g of an aqueous solution of trisodium citrate having a concentration of 30% by mass prepared using N ₂ bubbling water, washed (desalted), and then separated and collected by centrifugation. Similarly, the separated and recovered metal particles were immersed in 200 g of an aqueous solution of trisodium citrate having a concentration of 20% by mass prepared using N ₂ bubbling water and washed (desalted), and then separated and recovered by centrifugation again. .

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a concentration of 2.5% by mass in terms of metal was prepared using N ₂ bubbling water. Thereafter, deionization was performed using 10 g of the amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-3) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (P-3) was used.

[Example 4]
<Particle preparation process>
In the same manner as in Example 1, N ₂ micro-nano bubble water was prepared.
450 g of N ₂ micronano bubble water, 50 g of nickel nitrate hexahydrate (Ni (NO ₃ ) ₂ 6H ₂ O) (manufactured by Kanto Chemical Co., Ltd.), citric acid hydrate (organic stabilizer) (Kishida Chemical ( 0.5 g) was dissolved to prepare a solution A4.

50 g of sodium borohydride (reducing agent) was dissolved in 1000 g of N ₂ micro / nano bubble water to prepare a solution B4. While stirring the solution A4, the solution B4 was added and stirred for 1 hour. At this time, the liquid changed from green to black. Metal particles were separated and recovered from the obtained dispersion using a centrifuge.

<Washing process>
N ₂ bubbling water was prepared in the same manner as in Example 1.
The separated and recovered metal particles were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using N ₂ bubbling water and washed (desalted), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a concentration of 2.5% by mass in terms of metal was prepared using N ₂ bubbling water. Thereafter, deionization was performed using 10 g of the amphoteric ion exchange resin to obtain a black metal particle dispersion (P-4) having a concentration of 2.5% by mass in terms of metal.
<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (P-4) was used.

[Example 5]
<Particle preparation process>
In the same manner as in Example 1, N ₂ micro-nano bubble water was prepared.
400 g of trisodium citrate dihydrate was dissolved in 930 g of N ₂ micronanobubble water to prepare a solution (S5-1).
100 g of ferrous sulfate heptahydrate was dissolved in 500 g of N ₂ micro / nano bubble water to prepare a solution (S5-2).
Solution (S5-1) and solution (S5-2) were mixed and stirred for 30 minutes to prepare Solution A5.

A solution B5 was prepared by dissolving 57 g of silver nitrate (I) in 300 g of N ₂ micro / nano bubble water. Thereafter, the solution A5 was added to the solution B5, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours using a centrifuge.

<Washing process>
N ₂ bubbling water was prepared in the same manner as in Example 1.
The separated and recovered metal particles were immersed in 200 g of a trisodium citrate aqueous solution having a concentration of 20% by mass prepared using N ₂ bubbling water and washed (desalted), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and a metal particle aqueous dispersion having a concentration of 2.5% by mass in terms of metal was prepared using N ₂ bubbling water. Thereafter, deionization was performed using 10 g of the amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-5) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (P-5) was used.

[Example 6]
<Particle preparation process>
In the same manner as in Example 1, N ₂ micro-nano bubble water was prepared.
400 g of trisodium citrate dihydrate was dissolved in 930 g of N ₂ micro-nano bubble water to prepare a solution (S6-1).
180 g of ferrous sulfate heptahydrate was dissolved in 600 g of N ₂ micro / nano bubble water to prepare a solution (S6-2).
The solution (S6-1) and the solution (S6-2) were mixed and stirred for 30 minutes to prepare a solution A6.

A solution B6 was prepared by dissolving 76 g of copper (II) nitrate trihydrate in 600 g of N ₂ micro / nano bubble water. Thereafter, the solution A6 was added to the solution B6, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours using a centrifuge.

<Washing process>
The metal particles separated and recovered were immersed in 200 g of a 20% strength by weight trisodium citrate aqueous solution prepared using N ₂ micro / nano bubble water, washed (desalted), and then separated and recovered by centrifugation again.

The metal concentration was quantified by ICP analysis, and an aqueous metal particle dispersion having a concentration of 2.5% by mass in terms of metal was prepared using N ₂ micro-nano bubble water. Thereafter, deionization was performed using 10 g of the amphoteric ion exchange resin to obtain a black-brown metal particle dispersion (P-6) having a concentration of 2.5% by mass in terms of metal.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (P-6) was used.

[Comparative Example 1]
<Particle preparation and washing process>
N ₂ bubbling water was prepared in the same manner as in Example 1.
A metal particle dispersion (RP-1) was obtained in the same manner as in Example 1 except that this N ₂ bubbling water was used as a dispersion medium for the preparation and washing of the solution A1 and the solution B1, and the metal particle dispersion. .

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (RP-1) was used.

[Comparative Example 2]
<Particle preparation and washing process>
In the same manner as in Example 3 except that the N ₂ bubbling water used in Comparative Example 1 was used as a dispersion medium for the preparation and washing of the solution A3 and the solution B3 and the metal particle dispersion, the metal particle dispersion (RP- 2) was obtained.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (RP-2) was used.

[Comparative Example 3]
<Particle preparation and washing process>
In the same manner as in Example 4 except that the N ₂ bubbling water used in Comparative Example 1 was used as a dispersion medium for the preparation and washing of the solution A4 and the solution B4, and the metal particle dispersion, the metal particle dispersion (RP- 3) was obtained.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (RP-3) was used.

[Comparative Example 4]
<Particle preparation and washing process>
In the same manner as in Example 1 except that the N ₂ bubbling water used in Comparative Example 1 was used as a dispersion medium for the preparation and washing of the solution A3 and the solution B3, and the metal particle dispersion, the metal particle dispersion (RP- 4) was obtained.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (RP-4) was used.

[Comparative Example 5]
<Particle preparation and washing process>
CuCl ₂ powder, water as a solvent, CTAB as a dispersant, and citric acid as a protective agent that suppresses oxidation of copper nanoparticles were used. In a beaker with a volume of 100 ml, nitrogen was poured into the water, and with stirring, 1.0 × 10 ⁻² M copper chloride, 0.0364 g CTAB, 1.5 × 10 ⁻³ M citric acid were added. After mixing with water, 0.4M hydrazine was added as a reducing agent to prepare copper nanoparticles. The amount of water was adjusted so that the total amount of reagent and water added at this time was 20 ml. After stirring at room temperature for 3 hours, the obtained particles were subjected to centrifugal washing three times, and then a metal particle dispersion (RP-5) aqueous dispersion having a concentration of 2.5% by mass in terms of metal using pure water. Was prepared.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (RP-5) was used.

[Comparative Example 6]
<Particle preparation and washing process>
After mixing 0.1 mol of copper sulfate, 0.4 mol of sodium hypophosphite, 1 mol of PVP and 500 ml of ethylene glycol in a beaker and raising the temperature to 40 ° C., the mixture was dissolved using a stirrer to produce a mixed solution. . The prepared mixed solution was put into a microwave oven and irradiated with microwaves for 3 minutes. When a blackish brown reaction product was obtained by the reduction reaction, microwave irradiation was stopped, and 500 ml of distilled water cooled in advance was added to the mixed solution to quench it. After collecting black-brown copper nanoparticles by centrifugation and washing three times with acetone and distilled water, a metal particle ethylene glycol dispersion (RP) having a concentration of 2.5% by mass in terms of metal using ethylene glycol. -6) was prepared.

<Preparation of coating solution for coating formation and substrate with coating>
A coating liquid for forming a film and a substrate with a film were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion (RP-6) was used.

  The metal particle dispersion of the present invention is industrially useful because it can be used for forming a conductive film.

Claims (7)

A particle preparation step of preparing metal particles by reducing a metal salt in a liquid containing microbubbles;
A cleaning step of cleaning the metal particles with a cleaning liquid;
A method for producing a metal particle dispersion, comprising:   The metal salt is a salt of one metal selected from Group 4, Group 5, Group 8, Group 8, Group 10, Group 10, Group 11, Group 13, Group 14 and Group 15. The method for producing a metal particle dispersion according to claim 1.   The method for producing a metal particle dispersion according to claim 1 or 2, wherein the liquid containing microbubbles is water containing microbubbles.   The method for producing a metal particle dispersion according to claim 1, wherein the liquid containing microbubbles contains an organic stabilizer.   The method for producing a metal particle dispersion according to claim 1, wherein the microbubbles are bubbles containing a non-oxidizing gas.   The method for producing a metal particle dispersion according to any one of claims 1 to 5, wherein the cleaning liquid contains microbubbles.   A method for producing a coated substrate, comprising: coating a coating solution for forming a coating containing metal particles prepared by the method according to claim 1 on the substrate.